The typical mobile irrigation systems uses an overhead water distribution conduit which is supported by motorized towers that move the water distribution conduit over an agricultural field. Predominantly, such mobile irrigation systems are a center pivot type, in which the water distribution conduit is oriented radially with respect to a water supply pipe in the center of the agricultural field, and the motorized towers move the radially-extending water distribution conduit in a circular or arcuate path over the field. Linear mobile irrigation systems are also known, and such systems advance a laterally-extending water distribution conduit linearly across the field. Sprinkler nozzles attached to the water distribution conduit to shoot jets of water over long distances through the air to irrigate substantial expanses of the agricultural field. A significant portion of the emitted water is nebulized when the jet is created, resulting in a significant loss of water due to evaporation before the remaining water reaches the soil.
To reduce the amount of water lost to evaporation, drop lines have been attached to the overhead water distribution conduit. Spray heads are attached to the bottom ends of the drop lines a few feet above the soil and the growing plants. The spray from the heads does not extend great distances through the air, thus reducing the amount of water lost to evaporation. However the amount of water lost to evaporation is still significant, and even the sprayed water which reaches the plants is susceptible to some evaporation due in part to some of the water collecting on the leaves and evaporating before reaching the soil.
In a further effort to reduce evaporation, mobile drip irrigation systems have been devised to pull drip tubes through the agricultural field. The drip tubes are pulled along the soil from the moving water distribution conduit. Water is emitted directly from the drip tubes onto the soil. The emitted water quickly penetrates directly into the soil with little evaporation. The water is also less susceptible to displacement from its desired location of application due to the effects of wind.
Even though mobile drip irrigation systems are recognized as offering a greater potential for water conservation, previous mobile drip irrigation systems have not been widely accepted, despite their availability for many decades. The lack of acceptance is centered around uneven and unreliable water distribution coupled with many practical and operational problems associated with using previous mobile drip irrigation systems.
One problem of previous mobile drip irrigation systems is an inability to reliably and consistently control the paths taken by the drip tubes as they are pulled through the agricultural field. The drip tubes have a tendency to follow divergent and convergent pathways. When the pathways of adjacent drip tubes diverge, gaps and spaces occur in the field where little or no water is distributed. When the pathways of the drip tubes converge, excess water is applied to localized areas. Of course, those gaps with inadequate or no water do not promote the growth of the agricultural plants, but instead encourage the growth of naturally occurring weeds which diminish the overall quality of the agricultural production. Those plants which grow despite minimal irrigation are diminished in size and their maturity is delayed, which again diminishes the overall productivity from the agricultural field. Those spaces with excess water may prevent the germination and the optimal growth of the plants. Excess water may also create a hard exterior crust of soil known as “hardpan” which inhibits later-applied water from penetrating the soil effectively or which inhibits plant growth because of the difficulty of the growing plant to penetrate through the hard crust.
One operational problem which has plagued previous mobile drip irrigation systems is that the drip tubes frequently become tangled together due to the lack of control over the pathways taken by the drip tubes. The drip tubes may even become wound around the wheels of the motorized towers which move the overhead water distribution conduit through the field. Agricultural plants which have stiff stalks have the capability of tangling the drip tubes, thereby misdirecting the drip tubes from their intended movement pathways.
Reversing the direction of movement of mobile drip irrigation systems is necessary in those agricultural fields where a pivot mobile drip irrigation system does not circumscribe a complete circular pattern and where a linear mobile drip irrigation system reaches the end of the agricultural field. Reversing direction in previous mobile drip irrigation systems is particularly problematic because the reversal kinks or bends the drip tubes enough to choke off or substantially diminish water emission, even after the reversal in direction is completed.
The drip tubes of previous mobile drip irrigation systems are also susceptible to accelerated wear due to the friction of moving over the soil, particularly during cold weather and when used in sandy soil or soil which contains a large content of substantially sized solid particles. The frozen, sandy or particulate soil creates enough friction against the drip tubes as they move over the soil to wear unintended openings in the drip tube through which excess and uncontrolled water is delivered.
Manual intervention and repair is required to remedy the operational problems prevalent in previous drip irrigation systems. While taking the necessary corrective action, the mobile drip irrigation system is inoperative. Because of the persistent and repeating nature of these problems, the time required to undertake the corrective actions may reduce the amount of irrigation of the agricultural field as a whole to the point where the productivity of the agricultural crop is compromised.
Since water is a natural resource of ever-increasing scarcity, water conservation and more effective irrigation from the available amount of water are important requirements of modern agricultural irrigation.